1. Field of the Invention
This invention relates to a method of making optical mirrors, and more particularly concerns a casting method for making precision optical mirrors for telescopes, film projection systems, and other precision optic apparatus.
2. Description of the Prior Art
Precision optical mirrors have many uses, and, for example, are used in telescopes, projection apparatus, laser apparatus, spectroscopy, and holography, and are used in many types of optical experiments.
Normally, precision optical mirrors are made of glass and are hand polished, which makes them very expensive.
In a typical process for making an optical mirror, a slug of glass is first ground to a rough shape by a machine, and is then polished by hand until the glass meets precision optical requirements of accuracy, to within one-quarter of a wavelength of green light, or 5 millionth: of an inch.
Also, precision optical mirrors are usually made only in nearly spherical or flat shapes, because it is very difficult to polish glass to irregular or non-symmetrical shapes such as off-axis parabolic mirrors. In many cases, irregularly shaped mirrors are impractical because they are prohibitively expensive to make.